Relate voltage, electric potential energy and kinetic-energy gain.
Method and worked examples
Electric potential difference is potential-energy change per unit charge: ΔU=qΔV. The electric field does work Wfield =−ΔU, so an isolated particle’s kinetic-energy change is ΔK=−qΔV. A positive charge gains kinetic energy moving to lower potential; a negative charge gains kinetic energy moving to higher potential. The magnitude ∣qV∣ is often convenient when the stated voltage accelerates the particle.
One electronvolt is the energy gained by a charge of magnitude e through an accelerating voltage of one volt: 1eV=1.60×10−19J using the rounded constant. It is an energy unit, not a voltage or charge. Between broad parallel plates, away from edges, E=d∣ΔV∣ approximates a uniform field. The field points from higher toward lower potential.
Example 1
A proton moves through a potential decrease of 500V. Use e=1.60×10−19C.